In H.264/MPEG-4 AVC, one picture is divided into macroblocks to encode an image, the respective macroblocks are encoded by generating a prediction block using inter prediction or intra prediction. The difference between an original block and the prediction block is transformed to generate a transformed block, and the transformed block is quantized using a quantization parameter and one of a plurality of predetermined quantization matrices. The quantized coefficient of the quantized block are scanned by a predetermined scan type and then entropy-coded. The quantization parameter is adjusted per macroblock and encoded using a previous quantization parameter.
Meanwhile, in HEVC (High Efficiency Video Coding) under construction, various sizes of coding unit are introduced to obtain two times of compression efficiency. The coding unit has a role similar to the macroblock of H.264.
But, if the luma and chroma quantization parameter is adjusted per coding unit, the number of quantization parameters to be encoded increases as the size of the coding unit is smaller. Therefore, adjusting luma and chroma quantization parameter per coding unit results in greater quantity of coding bits required to encode the quantization parameter, which degrades the coding efficiency. Also, because using various sizes of coding unit makes the correlation between the quantization parameter and the previous quantization parameter weaker than that of H.264, a new method of encoding and decoding the quantization parameter is required for various sizes of the coding unit. Accordingly, more effective method is required to encode and decode the image for luma and chroma component.